Nursing Entrance Exam (NEX) Practice Exam

Which organism has the most complex digestive system?

1. Earthworm

2. Planaria

3. Amoeba

4. Hydra

The correct answer is: Earthworm

The earthworm has the most complex digestive system among the organisms listed. Its digestive system is a complete one, meaning it has two separate openings for the intake of food and the expulsion of waste. This system is divided into specific regions, each specialized for different functions in the digestive process. It starts with the mouth, where food is ingested, and progresses through the pharynx, esophagus, gizzard, and intestine, finally leading to the anus. The gizzard is particularly noteworthy, as it grinds up the food to aid digestion, and the intestine is typically where nutrients are absorbed. This organization allows for a more efficient digestion process compared to other organisms that have less specialized or incomplete digestive systems. In contrast, planaria possess a gastrovascular cavity, which serves both digestive and circulatory functions, but lacks the complexity of a complete digestive tract. Similarly, amoeba utilizes phagocytosis to ingest food, which is digested intracellularly, and hydra has a simple gastrovascular cavity without the specialization seen in earthworms. Thus, the earthworm's sophisticated structure and function of its digestive system make it the most complicated among the options provided.